for Freud, is analogous to the way the psychic system which received sense impression from the outside world remains unmarked by those impressions which pass through it to a deeper layer where they are recorded as unconscious memory. Thus, "the appearance and disappearance of the writing" is similar to "the flickering-up and passing-away of consciousness in the process of perception" (SE XIX:230).

Freud's somewhat off-hand analogy of the way which the perceptive conscious passes experience through to the unconscious to a child's toy has had a curious career. In "Freud and the Scene of Writing," Derrida notes the father of psycho-analysis's dependence on metaphors of writing to describe psychological processes and concludes that this is no metaphor, that perception really is a kind of writing machine like the Mystic Writing Pad. Derrida in particular notes the fact that the marks on the pad are not visible due to the stylus leaving a deposit on the sheet of plastic (in the manner of a pen, ink and paper). The marks only become visible because of the contact the wax has on the reverse side of the sheet of plastic...
In hypertext, consciousness is displaced from the act of apprehension, from the act of reading, to experience of having been written.